Internal combustion engine torque measurement device and method

ABSTRACT

This method includes detecting the passage before a sensor of each of the teeth of the inertial flywheel of an engine; measuring the time of passage d i  of each of these teeth; constituting a measurement horizon extending on both sides of the angular range of the explosions; dividing this measurement horizon into eight sets of teeth of equal length of which six are for the angular range of the explosions; measuring the passage times of these eight sets and in assigning them a rank in the measurement horizon du +1 , du 0 , . . . , du 5 , du +1  ; calculating the period of the explosions T=du 0  +du +1  +du 2  +du 3  +du 4  +du 5  ; calculating a term Q c  =2du 0  -du -1  -du 3  -du +1  +2du 5  ; calculating a term D c  =p·Q c  where p=π/2√3, a constant stored in a memory; and calculating the desired torque using the relation Cg c  =A·D c  /T 3  +B/T 2  in which A and B are constants stored in a memory.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a method and a device for measuring the torque ofan internal combustion engine and, more precisely, to improvements tothis method and device for measuring the aforementioned torque asdescribed in French Patent No. 9,111,273 filed by the applicant.

2. Discussion of the Background

In this patent a device is described to produce a numerical value Cgwhich is representative of the mean gas torque generated by eachcombustion of the gaseous mixture in the cylinders of a combustionengine at low level operating conditions. This device comprises:

measurement references arranged on a ring gear which is integrallyconnected to the inertial flywheel of the engine or the shaft;

means to define at least one reference for indexing the reference;

a sensor which senses the passage of the references and which is mountedin a fixed manner in the vicinity of the ring gear;

calculation means to produce a primary numerical value d_(i), which isrepresentative of the instantaneous passage time before the sensor ofeach of the references;

calculation means to derive from the primary numerical values d_(i) asecondary numerical value T which is representative of the total passagetime before the sensor of each series of n references in the angularrange of the combustions of the engine;

calculation means to derive a second secondary numerical value D, whichis representative of the projection onto a phase reference line of thereferences, corresponding to the origin of the angular periods of thecombustions, of the amplitude of the alternating component of theinstantaneous passage times di of the references before the sensor, atthe frequency of the combustions in the engine. The defining relation Dis: ##EQU1## hereafter called the initial relation calculation means toderive the desired numerical value Cg from the relation Cg=A·d d/T³+B/T², where A and B are experimentally determined constants.

In a variant, the same patent proposes, to decrease the calculationtimes, to regroup the n references of an angular range of combustionsinto three or four sets and to calculate the above-mentioned term D fromthe passage times of these sets before the sensor.

SUMMARY OF THE INVENTION

A first object of the invention is to propose a method and device forsimplified calculation of the term D, using a small number of referencesets and producing a result which is essentially identical to thatsupplied by the initial calculation procedure, while at the same timeconsiderably decreasing the number of mathematical operations required.

A second object of the invention is to propose a method andcomplementary device either of the fundamental method described in thepatent referenced above, or of the method and device according to thefirst object of the present invention, to measure the variations at alow frequency of the resistant torque applied to the engine to allow theassignment of a quality factor to the torque measurement performed.

A third object of the invention concerns a method and device derivedfrom the preceding ones to correct the low-frequency perturbationsundergone by the engine torque, especially those caused by theoscillations of the vehicle or by sudden changes in load.

A fourth object of the invention is to propose a method and device tocarry out a new correction integrating the effects of the richness ofthe mixture of the recirculation rate, of the exhaust gases and of thetransient operating conditions of the engine. This new correction may ormay not be combined with the above-mentioned corrections.

According to a first object of the invention, a method for thecalculation in a simplified manner of the term D mentioned aboveconsists in:

establishing a measurement horizon equal to at least the angular rangebetween consecutive explosions in the engine;

regrouping the instantaneous passage time di of the references containedin this measurement horizon in a relatively small number of du₀, . . . ,du_(m) passage times of reference sets and in assigning to these timesdu their rank 0 . . . m in each measurement horizon;

combining together, by addition and subtraction, possibly weighted, anumber of times having predetermined ranks, so as to produce a magnitudeQ which has a nonzero frequency response at the analysis frequency ofthe explosions of the engine;

determining a weighting constant such that the frequency response of theterm D=p.Q is at least for said analysis frequency and for thecombination of the measurements used for Q, identical to that obtainedfor the term D calculated by said initial relation.

According to a first embodiment of the preceding method, the measurementhorizon exactly corresponds to the angular interval separating twoconsecutive explosions of the engine, the number of reference sets beingsix and the six measurement times referenced du₀, . . . , du₅, themagnitude Q=(du₀ +du₅ -du₂ -du₃) and the constant p=π/2√3, when thereference sets have the same angular length π/6.

Thanks to this simplified calculation method, the value obtained for theterm D is essentially identical to that initially obtained, and thisapplies in spite of the fact that the number of arithmetic operations tobe performed has been reduced to four. This considerably reduces thespecifications of the microprocessor used to perform the calculations.Moreover, it should be immediately noted that the practical embodimentforms of the methods according to the invention are determined by asystematic analysis of the mathematical equivalents of the initialrelation which defines D.

In a second embodiment of the method, the measurement horizon is equalto the above defined horizon, increased by an additional packet du₆, theterm Q then being equal to Q=du₀ -du₃ +3/2. (du₆ -du₄). The second formhas the advantage of improved discrimination between late combustionsand combustion misses of the engine.

According to the second object of the invention, a method to measure thevariations δCg of the resistant torque applied to a two- orfour-cylinder engine consists in:

establishing a measurement horizon which is equal to at least theangular range between two consecutive explosions in the engine;

regrouping the instantaneous passage times di of the referencescontained in this measurement horizon in a relatively small number ofdu₀, . . . , du_(m), passage times of reference set and identify thesetimes du by their rank 0 . . . m' in each measurement horizon during thecourse of an analysis, the angular values of the time sets of ranks 0and m' being equal;

assigning the reference du₋₁ to the time of the last reference sets ofthe last measurement horizon analyzed before and the reference du+₁ tothe time of the first reference sets of the next measurement horizon tobe analyzed;

combining four of these data elements du using the relation q=δu=(du₀-du₋₁ +du_(m') -du₊₁);

deriving the desired term δCg using the relation δCg=a.q.A/T³, where ais a new constant which is dependent on the angular value of the fourreference sets concerned.

According to a first embodiment of this method, the angular length ofeach reference set is π/6 and the constant a=π/2√3.

According to the third embodiment of the invention, a method to producea value of the term D defined above, with corrections for low-frequencyperturbations which affect the engine because of changes in resistanttorque applied to this engine, consists in calculating this valueaccording to the relation

Dc=pQ+aq, where a and p are two constants which may be identical.

The implementation of this third method is particularly simple andeffective, due to the considerations indicated below.

The calculation of the mean gas torque Cg expressed by the fundamentalrelation Cg=A·D/T³ +B/T² remains valid for as long as the load appliedto the engine is decoupled for the analysis frequency considered.However, at low levels of rotation, the analysis frequency approachesthe oscillation frequency of the load. In the case of strong variationsin the load (sudden demand for torque, oscillation of the vehicle on aroad in poor condition, initiation of transmission resonance), thecalculation of the mean gas torque is perturbed according to therelation:

Corrected Cg=measured Cg -k·dC_(c) /dθ, where C_(c) is the resistanttorque applied to the engine (the load) and k, a constant equal to theratio of the mean gas torque to the component of the instantaneous gastorque at the analysis frequency. In the case where the measurementhorizon is one-half turn or a complete turn, the limits of this horizoncorrespond to dead center for all cylinders. The torque exerted on theshaft by the pressure existing in the cylinders is thus zero since thelever arms are zero at that instant. The load applied to the shaft canthen be calculated by measuring the acceleration of the flywheel aboutdead center.

Let d-and d+be the times corresponding to an angle d_(r) on both sidesof dead center. The load applied to the flywheel is then: C_(c) =J·π³/dθ² ·(d+-d-)/T³, where J is the total inertia of the flywheel and theshaft. By using C_(c-) and C_(c+) to designate the torques so calculatedrespectively at the beginning and the end at the end of a measurementhorizon, the instantaneous variation of the load torque affecting themeasured torque Cg is

    δCg=k·(C.sub.c+ -C.sub.c-)/π.

    Corrected Cg=measured Cg-k·(C.sub.c+ -C.sub.c-)/π.

From the times of the sets with angular length π/6 and, taking intoaccount that the term A of the relation defining Cg and that the terms kand J above are connected, the variation of the load torque can bewritten, with good precision:

    δCg=(π/2√3)·(du.sub.0 +du.sub.5 -du.sub.-1 -du.sub.+1)·A/T.sup.3.

Any nonzero value of this term δCg is a factor which negatively affectsthe quality of any measurement of Cg performed at that instant.

From the value of δCg it is in addition possible to directly apply acorrection to the term D indicated above and to write (a=p=π/2√3):

    D.sub.c =P(Q+q)=π/2√3·(2du.sub.0 -du.sub.-1 +2du.sub.5 -du.sub.3 -du.sub.+1)

and

    Cg.sub.c =AD.sub.c /T.sup.3 +B/T.sup.2.

Under these conditions, by means of a simple complementary calculation,the corrected mean gas torque Cg_(c) calculated from the corrected termQ_(c) is insensitive to variations at low pressure of the resistanttorque for as long as the approximation of this torque by a parabolaremains valid within the measurement horizon. This is the case for aslong as the value of the term δCg remains relatively low, whichcorresponds to the absence of either large perturbations of theresistant torque applied to the engine or abrupt changes of largeamplitude affecting this torque. The term δCg can quite clearly beproduced independently of the term D. In this case, it constitutes anegative quality factor for the torque Cg, regardless of the manner inwhich this torque is calculated.

According to the fourth object of the invention, the method used to takeinto account the particular conditions of a combustion affecting thedetermination of the numerical value Cg of the mean gas torque generatedby each combustion of gaseous mixture in the cylinders of a four-strokeand four-cylinder combustion engine at low-level operating conditions,and consequently to correct this numerical value, which is expressed bythe relation: Cg=A·D/T³ +B/T², is characterized in that it consists in:

determining the air mass M pumped in a cylinder during the period ofcombustion of another cylinder;

determining the pumping torque Cp required for this purpose;

storing in memory these two data element during the following twocombustion periods;

combining this data to produce a correction term H_(n'), for the torqueCg_(n'), which pertains to the combustion period of rank n' according tothe relation:

    H.sub.n' =-δ·(M.sub.n'-2 +M.sub.n'-1)+α·Cpn'.sub.-2 ;

in which δ and α are constants which depend on the type of engine, and

calculating the corrected mean gas torque, generated during thecombustion period of rank n', according to the relation Cg_(cn')=h·Cg_(n') +H_(n'), where h is a calibration constant which is dependenton the type of engine.

According to a particular characteristic of the method according to theinvention:

determination of the air mass M consists in measuring the pressure Pc inthe air-intake manifold of the engine and in calculating M=Pc·R_(N),where R_(N) is the essentially constant filling coefficient of thecylinders of the engine;

determination of the pumping torque Cp consists in measuring theatmospheric pressure Pa and in calculating Cp=(Pc-Pa).

The implementation of this particular characteristic of the methodaccording to the invention makes it possible to express the term H_(n')according to the relation:

    H.sub.n' =-δ·R.sub.N (Pc.sub.n'-2 +Pc.sub.n'+1)+α·(Pc.sub.n'-2 -Pa).

Due to these arrangements, a correction is applied to the measurement ofthe torque of a four-stroke engine with four cylinders, which correctionis adapted to the operation with a lean mixture, to a high recirculationrate of the exhaust gases and/or to the transitory conditions of theengine (variation in the butterfly valve angle). All these advantagesresult from the considerations indicated below.

The torque exerted by the pressure of the gases on the crankshaft is theresultant of the torque applied by the cylinder in the expansion phaseand of the torque applied by the cylinder in the compression phase. Inthe case of a theoretical thermodynamic cycle, the two expansion andcompression torques are adiabatic, and thus identical to the nearestfactor k (k increases when the combustion energy, and thus the richness,increases).

In the case of a four-stroke four-cylinder engine, if C_(comp) (θ)represents the instantaneous torque exerted by the cylinder in thecompression phase, the torque exerted by the cylinder in the expansionphase is then equal to:

    c exp=k·C.sub.comp (π-θ).

The gas torque is the sum of the expansion torque, the compressiontorque (negative because resistant) and of the pumping torque. Pc beingthe pressure in the intake manifold and Pa the atmospheric pressure, itis possible to consider the pumping torque to be proportional to(Pc-Pa). The gas torque is thus:

    C.sub.gas =C.sub.exp -C.sub.comp +α·(Pc-Pa)=(k-1)·C.sub.comp +α·(c-Pa).

In the case of a computer estimation of the torque Cg defined by therelation indicated above, the symmetry of the curve of the coefficientswith respect to the median plane of the measurement horizon istransformed into a curve with odd symmetry with respect to the torque.The result is that the resistant compression torque is considered apositive torque, just like the expansion torque, by the method formeasuring Cg. The measured value of the torque is:

    Cg=A·D/T.sup.3 +B/T.sup.2 =β·(C.sub.comp +C.sub.exp).

However, the compression torque C_(comp) can be calculated from the airmass introduced into the cylinder, which can be derived, either from ameasurement with a flowmeter or from a compression measurement. In thecase of the pressure, the compression torque is proportional to thepressure Pc in the manifold and to the filling coefficient R_(N) of thecylinder of the engine (which depends on the operating condition of theengine):

    C.sub.comp =δ·R.sub.N ·Pc.

In the case of the generated gas torque, the torque C_(comp) is thecompression torque of the cylinder which will be in the expansion phaseat the time of the measurement (pressure Pc.sub.(n-2), whereas for Cg,the measured gas torque, the torque C_(comp) of the cylinder in thecompression phase is measured at the time of the measurement (pressurePc.sub.(n-1). In contrast, the filling coefficient can be the same forthe two cylinders because there is little variation in the operationscondition of the engine. By combining the above equations, we get:

    Cg.sub.c =C.sub.exp -C.sub.comp +α(Pc.sub.(n-2)-Pa)

or

Cg_(c) =h·Cg+H, where h is a calibration constant which is a functionthe type of engine, and:

    H=δ·R.sub.N ·(Pc.sub.(n-1) +Pc.sub.(n-2) +α(Pc.sub.(n-2) -Pa),

in which α=V/π, where V is the unitary displacement of the engine, andδ=1.14V in a first approximation (with k=4.5) adjustable for each typeof engine and filling coefficient R_(N) filling coefficient of theengine, which is dependent on the operating conditions but is equal to 1in a first approximation (it varies from 0.8 to 1.02 as a function ofthe increasing operating conditions).

It is recalled that the term R_(N).PC represents the air mass introducedinto the cylinder. Consequently it can be replaced by another Da/Nestimator, where Da is the flow rate of the air mass in the manifold andN is the number of turns per second of the crankshaft. Similarly, theterm (Pc-Pa) can be replaced by (D·T-M₀) , where M₀ is the air massintroduced into a cylinder for a fully-opened butterfly valve.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and the advantages of the invention will become moreprecise in the description of a particular embodiment of the inventiongiven below as a nonlimiting example, with reference to the drawings inthe appendix, in which:

FIG. 1 is a diagram of the different elements which constitute themeasurement device according to the invention;

FIG. 2 represents the frequency responses of the two D terms, calculatedby means of the initial relation and the simplified relation,respectively;

FIG. 3 represents four implementation and operation waveforms ofteeth-references packet times;

FIG. 4 represents the diagram of the different elements which constitutea second embodiment of a device for measuring the torque of an engine,according to the invention; and

FIG. 5 represents the diagram of the elements specific to a thirdembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to FIG. 1, a circuit 10 is represented, for the measurement ofthe mean gas torque Cg_(c), corrected for low-frequency perturbations,which is produced by each combustion of the gaseous mixture in afour-stroke four-cylinder combustion engine equipped with a toothedmeasurement ring gear 12 which is integrally connected to the flywheelof an engine with electronic ignition. For example, the ring gear 12includes, a its perimeter, fifty-six identical teeth which are regularlyspaced, such as those formed by the solid part 14 and the recessed part16, distributed into two series of twenty-eight teeth separated by twodiametrically opposite reference teeth, such as the ring gear formed bythe solid part 18 and the recessed part 20 which have a width which istwice that of the other teeth. In fact, the ring gear 12 comprises(2×28+2×2)=60 equidistant references which are made up of real orvirtual teeth of the same module. The two broad teeth which arediametrically opposite are used as reference or origin of indexation toallow the numbering of each of the teeth and especially theidentification of the tooth do which will be defined below.

With the four-stroke four-cylinder combustion engine referred to in theexample above, it should be noted immediately that the angular period ofthe combustions concerns 30 teeth and it is equal to half the period ofrotation of the crankshaft.

A fixed sensor 22 is associated with crown 12, for example, one withvariable reluctance, which is adapted for the delivery of an alternatesignal 24 having a frequency proportional to the speed of passage of theteeth of the ring gear that is proportional to the instantaneous speedof the flywheel.

The angular position of this sensor 22 with respect to the indexingteeth 18 at the time when the piston of a cylinder is at top dead centeris known or determined. This allows the identification of the tooth doas being the one which passes before the sensor during the passage ofthe piston of a given cylinder through its top dead center ofcombustion. The signal delivered by the sensor 22 is applied to theinlet of a shaping circuit 26 which is adapted to the delivery ofsignals 28 with steep edges, having a period equal to the instantaneousperiod d_(i) of the incident signals 24, the index i varying from 0 to29 as the teeth pass before the sensor. Each period d_(i) of the signalso produced corresponds to the passage time of one tooth, either a solidpart or a recessed part, before the sensor 22. As far as the incidentsignals produced by the reference teeth 18 are concerned, the shapingcircuit 26 transforms them in the same manner into a signal with steepedges, having a time which is exactly twice that of the signalspertaining to the other teeth. The signals 28 are applied to a stage 30for the measurement and the calculation of the instantaneous periodsd_(i) of passage of the real and virtual teeth of the measurement ringgear 12 before the sensor 22.

The measurement and calculation stage 30 comprises counting circuitswhich receive high-frequency timing pulses (10 MHz, for example)produced by a quartz clock 32 and it delivers at the output numericalvalues which are representative of the number of clock pulses countedbetween two low-high transitions of the signals with steep edgesproduced by the shaping stage 26. As far as the processing of eachsignal 28 produced by one of the long indexing teeth 18-20 is concerned,in the context of the described example, its value will be divided bytwo (one-bit shift) , and the result will be assigned to thecorresponding virtual teeth. In this manner, the stage 30 for themeasurement and calculation of the periods d_(i) sends a successiveseries of thirty numerical values d_(i) to a buffer memory 34, which arerespectively associated with thirty consecutive numbers ranging from 0to 29 defining the rank i of each of the real or virtual teeth within ameasurement horizon.

The buffer memory 34 is connected to a calculation stage 36 which isadapted for regrouping the thirty instantaneous times d_(i) between tworeference teeth in sets of fine. In this manner, the stage 36successively produces six passage times of five teeth-reference sets,respectively bearing the numbers du₀, . . . , du₅ as they are produced.These six times and their six rank numbers are represented in line I ofFIG. 3. These times and these numbers are then transmitted to a buffermemory 38 which is placed under the control of a transfer control stage40 which is also adapted for receiving the times du₀, . . . , du₅, andidentifying the rank of the time du₀.

The buffer memory 38 is adapted to contain three successive series ofsix times of sets-references: a central series which defines themeasurement horizon during the analysis, a front series which precedesthe central series in time and a rear series which follows it. When anew time du₀ arrives, the transfer control stage 40 is adapted so as totransfer to the following stages the six reference times du₀, . . . ,du₅ of the central series as well as, under the reference du₋₁, the timedu₅ of the last set of the preceding series and, on the reference du₊₁,the time du₀ of the first set of the series which has just arrived. Thisis represented in line II of FIG. 3.

A first calculation step 42 which receives these eight successive timesis programmed so as to select the six reference times du₀, . . . du₅ andto calculate from them the sum, which is the instantaneous period T ofan angular range of combustions. Each new value T so calculated isaddressed to a buffer memory 44 where it replaces the value calculatedearlier.

A second calculation step 46, which receives these eight successivetimes (du₋₁, du₀, . . . , du₅, du₊₁) is programmed to select the fourfollowing times: du₀, du₂, du₃ and du₅, and du₅, and to combine themaccording to the relation represented with the signs and the weightingsin line II of FIG. 3:

    Q=(du.sub.0 -du.sub.2 +du.sub.5 -du.sub.3).

A third calculation stage 47 which receives the same eight times isprogrammed to select the four time du₋₁, du₀, du₅ and du₊₁ and tocombine them according to the relation: q=δu=(du₀ -du₋₁ +du₅ -du₊₁).

The terms Q and q so calculated are addressed to a buffer memory 48where they remain until new values of Q and q arrive. The buffer memory48 is connected to a fourth calculation stage 50 which also receivesfrom a memory 52 the weighting constant p=a=π/2√3. The calculation stage50 is adapted for calculating the sum Q_(c) =Q+q, and then the productD_(c) =p·Q_(c), and to apply it to a fifth calculation stage 54.

This calculation stage 54 also receives from a memory 56, two constants,A and B, experimentally determined and, from the buffer memory 44, theterm T. From these four magnitudes, the stage 54 calculates the mean gastorque, corrected for low-frequency perturbations according to therelation Cg_(c) =A·D_(c) /T³ +B/T². As a consequence of what has beensaid above, it should be noted that this value Cg_(c) so calculatedapplies only to two- or four-cylinder engines, in which high or low deadcenter occurs with every turn or every half turn of the crankshaft,depending on whether the engine is a two-stroke or four-stroke engine.For engines with six or eight cylinders, for example, the correction ofthe mean gas torque for at low-frequency perturbations will no longer bepossible. In this case, the buffer memory 38 will be limited to a seriesof six sets of teeth-references and the calculation stage 42 will beadapted so as to perform only the calculation of Q=(du₀ -du₂ -du₃ +du₅).

With Q_(c) =Q+q, the correct mean gas torque Cg_(c), calculated asindicated above, comprises two elements, that is the torque Cg measuredaccording to the simplified relation using the term

Q=(du₀ -du₂ -du₃ +du₅) and a correction δCg applied to this torque Cg someasured, using the term

    q=(du.sub.0 -du.sub.-1 -du.sub.+1 +du.sub.5).

Consequently, the precision of the measurement of the torque Cg, whichis carried out from the simplified relation using the term Q, isreplicated entirely in the measurement of the torque Cg_(c) correctedfor low-frequency perturbations. In contrast, this is not the case withperturbations at frequencies which are much higher than the frequenciesof the combustions. For these high-frequency perturbations, neither theinitial calculation procedure nor the simplified calculation procedureaccording to the first object of the present invention allows theircorrection, the simplified calculation procedure being in that caseworse than the initial calculation procedure. These different resultsclearly appear in FIG. 2 which represents the frequency response of thetwo terms D calculated respectively according to the two procedures inquestion. Indeed, these frequency responses are identical up to fourtimes the frequency of a measurement horizon 2Ωo (Ωo being the frequencyof rotation of a four-stroke, four-cylinder engine). At higherfrequencies, the frequency response of the term D, obtained using thesimplified calculation procedure, presents amplitude maxima which aremuch greater than those of the term D obtained by the initialcalculation procedure. This signifies that the high-frequencyperturbations are taken more into account by the simplified calculationprocedure than by the initial procedure.

According to this FIG. 2, it is verified that the magnitude Q has anonzero frequent frequency at the analysis frequency of the explosionsof the engine, and a nonzero frequency response at zero frequency, thatis a zero value for a strictly constant speed of rotation of the engine,which is essential for the quality of the approximation D=pQ.

In an embodiment variant of the method, the measurement horizon is equalto the horizon defined earlier, increased by an additional set du₆, forexample, du+1, the term Q in that case being equal to Q=du₀ -du₃+3/2·(du₆ -du₄) . This second form has the advantage of improvediscrimination between late combustions and combustion misses of theengine.

The term q is still provided by the relation q=δu=(du_(o) -du₋₁ +du₅-du₊₁), however, the weighting constants a and p used for thecalculation of Dc are then different, a remaining equal to π/2√3 and passuming a value which is determined experimentally.

As indicated in the preamble of the present description, the formulaused for the calculation of the mean gas torque, that is Cg=A·D/T³+B/T², is only valid for engines in low-level operating conditions. Inthe case of an engine in high-level operating conditions, a correctionmust be applied to the coefficient A in question, as indicated in thepatent referred to in this preamble. For this purpose, the coefficient Ais replaced by A_(c) =A(1-z) where z=(fi/fr)². In this equation fi =1/T,the instantaneous frequency of the combustions and fr is the torsionalresonance frequency of the shaft/inertial flywheel connection. To applythis correction in the context of the present invention, the memory 56will contain the constant term fr and the calculation stage 54 willcalculate fi=1/T and then z=(fi/fr)² and then A_(c) =A(1-z), and then,finally, the desired value Cg_(c) =A_(c) ·D/T³ +B/T², which, in thiscase, is both valid for low- and high-level operating conditions of theengine and correct for low-frequency perturbations.

The invention is not limited to the embodiment described with referenceto FIG. 1 and to lines I and II of FIG. 3. Indeed, it is possible toreplace the eight weighted times of the sets-references of line II ofFIG. 3 by the eight other weighted times of line III of the same figure.In this case, the times which are not taken into account in thecalculation of Q'_(c), that is, du₁ and du₄, concern six teeth and theother times, seven teeth. Consequently, the times du₀ and du₅ eachconcern two teeth within the angular range separating two consecutivehigh dead centers and five teeth outside of this range. The relationconnecting Q'_(c) to the times du₋₁, du₀, . . . , du₅, du₊₁, representedin line III of FIG. 3, is the same as that connecting Q_(c) to thesesame times represented in line II of this figure. These two relationsare illustrated with the signs and weightings in these lines II and III.Similarly, in line IV of FIG. 3, a continuous series is represented, offour times of sets-references du₀, . . . , du₃ each concerning eightteeth, the times du₀ and du₅ each including one tooth outside theangular range separating two consecutive high dead centers.

In the case of line III of FIG. 3, the number of sets teeth taken intoaccount and those sets not taken into account, as well as the weightingsand the signs of the times of sets taken into account are determined sothat the simplified calculation term Q'=(du₀ -du₂ -du₃ +du₅) presents anonzero mean value during one measurement horizon and a nonzerofrequency response at the frequency of this horizon. A constantweighting coefficient p' is then applied to the term Q' so that thefrequency response of the term D=p'·Q' at the frequency of themeasurement horizon is identical to that supplied for this term Dobtained by the initial calculation procedure. The three parametersindicated above (numbers of teeth, weightings and signs of the sets) arealso determined so that the frequency response of the term D=p'·Q' atfrequencies greater than the measurement horizon frequency is as low aspossible. Moreover, for the calculation of the term q' for correction ofthe low-frequency perturbations, the expression defining q' is identicalto that of q indicated above, and the numbers of the teeth of the setswhose times are referenced by du₋₁ and du₊₁ are the same as those of thetimes referenced du₀ and du₅, as appears in line III of FIG. 3.

All the above considerations, which concern Q' and p', apply to theentire embodiment presented in line IV of FIG. 3, the value of Q' thenbeing Q'=(du₀ -du₁ -du₂ +du₃)

In the two cases illustrated in lines III and IV of FIG. 3, thepreparation of the necessary magnitudes for the calculation of theangular period T of the combustions of the engine will be modified totake into account the fact that the measurement horizon extends beyondboth sides of the angular range concerned. This preparation will consistin calculating in addition to the times necessary for the calculation ofQ' and Q'_(c), times du_(0t) and du_(5t) (for the example of line III)or du_(3t) (for the example of line IV) which are times du₀, du₅ and du₃which have been truncated and limited only to those teeth within thisangular range. For this purpose, the stage 36 for the measurement of thetimes of the sets and for the identification of their ranks describedabove will calculate in addition these truncated times and assign anadequate identification to them. The stage 42 for the calculation of theperiod T will be programmed accordingly.

In a variant, it is noted that the two sets of times du₂ and du₃ in thecase of lines I, II and III of FIG. 3, and those of times du₁ and du₂ inthe case of line IV, can be grouped into a single set by the stage 36.The calculations of T and of Q_(c), which follow, will be modifiedaccordingly.

It is noted that the angular range defining the width of the sets ofrank 0 and m' determines the precision of the measurement of δCg. Whenthis range is relatively small, this precision decreases. When itbecomes relatively large, the measurement becomes sensitive to thepressures in the cylinders. This is due to the fact that the lever armsof the connecting rods are no longer negligible and, in this case, theset of rank m' of the measurement horizon analyzed before (its time isreference du₋₁) and that of the rank 0 of the following horizon (itstime is reference du₊₁) are at a significant distance from the twoconsecutive high dead centers which determine the theoretical boundariesof the measurement horizon during an analysis. To correct this negativeeffect of the broadening of the sets of rank 0 and m', it is possible tointroduce a slight angular shift of the measurement horizon during ananalysis by slightly advancing beyond the boundaries of this measurementhorizon with respect to the two high dead centers which define themtheoretically. The purpose of this is to gain some distance from theeffects of the combustion.

It is recalled that the calculation of the negative quality factor δCgof the torque Cg can be carried out regardless of how the term Cg iscalculated, in the simplified or unsimplified form, and that, inaddition, it can be made available, as is to the user. For this purpose,an additional calculation stage 55 will be provided which receives afrom the memory 52, q from the memory 48, A from the memory 56 and Tfrom the memory 44, and which calculates δCg=a·q·A/T³.

A circuit 10 is represented in FIG. 4 for the measurement of thecorrected mean gas torque in a first step of the low- and high-frequencyperturbations produced by each combustion of the gaseous mixture in afour-stroke, four-cylinder combustion engine operating at low and highoperating conditions (Cg_(c1)) and, in a second step, of theperturbations affecting the measurement because of the particularconditions of the combustions in the engine (Cg_(c2)).

For this purpose, a toothed measurement ring gear 12 is mounted, withintegral connection, on the inertial flywheel of an engine withelectronic ignition. For example, the ring gear 12 comprises, on itsperiphery, fifty-six identical, regularly spaced, teeth, such as thoseformed by the full part 14 and the hollow part 16, distributed into twoseries of twenty-eight teeth separated by two diametrically oppositereference teeth, such as the tooth formed by the solid part 18 and thehollow part 20, which have a width that is twice of that of the otherteeth. Indeed, the ring gear 12 comprises (2×28+2×2)=60 equidistantreferences consisting of real or virtual teeth of the same module. Thetwo diametrically opposite broad teeth serve as reference or origin ofindexation to allow the numbering of each of the teeth and especially toidentify the tooth d₀ which will be defined below.

With the four-strokes, four-cylinder combustion engine mentioned above,it is immediately noted that the angular period of the combustionsconcerns thirty teeth and is equal to half the period of rotation of thecrankshaft.

A fixed sensor 22 is associated with the ring gear 12, for example, onewith variable reluctance, which is adapted for the delivery of analternating signal 24 with a frequency proportional to the rate ofpassage of the teeth of the ring gear, that is proportional to theinstantaneous speed of the flywheel.

The angular position of this sensor 22 with respect to the indexingteeth 18 at the time when the piston of a cylinder is at top dead centeris known or determined. This allows the identification of the tooth d₀as the one which passes before the sensor during the passage of thepiston of the given cylinder at its high dead center of combustion. Thesignal delivered by the sensor 22 is applied to the input of a shapingcircuit 26 which is adapted for the delivery of signals 28 with steepedges, having a time equal to the instantaneous period d_(i) of theincident signals 24, the index i varying from 0 to 29 as the teeth passbefore the sensor. Each period d_(i) of the signal so producedcorresponds to the passage time of a tooth, either a solid part or ahollow part, before the sensor 22. As far as the incident signalsproduced by the reference teeth 18 are concerned, the shaping circuit 26transforms them in the same manner into a signal with steep edges,having a time that is exactly twice that of the signals assigned to theother teeth. The signals 28 are applied to a stage 30 for measurementand calculation of the instantaneous periods d_(i) of passage of thereal and virtual teeth of the measurement ring gear 12 before the sensor22.

The measurement and calculation stage 30 comprises counting circuitswhich receive high-frequency timing pulses (10 MHz, for example)produced by a quartz clock 32, and it delivers numerical values at theoutput which are representative of the number of clock pulses countedbetween two low-high transitions of the signals with steep edgesproduced by the shaping stage 26. As far as the processing of eachsignal 28 produced by one of the long indexing teeth 18-20 is concerned,in the context of the described example, its value will be divided bytwo (one-bit shift) and the result will be assigned to the twocorresponding virtual teeth. In this manner, the stage 30 for themeasurement and the calculation of the periods d_(i) addresses to abuffer memory 34 successive series of thirty numerical values d_(i),respectively associated with thirty consecutive numbers ranging from 0to 29 defining the rank i of each of the real or virtual teeth within ameasurement horizon.

The buffer memory 34 is connected to a calculation step 36 which isadapted for regrouping, in sets of five, the thirty instantaneous timesd_(i) between two reference teeth. In this manner, the stage 36successively produces six passage times of five teeth-reference sets,respectively numbered du₀, . . . , du₅ as they are produced, the angularvalue of each set being π/6, these times and numbers are thentransmitted to a buffer memory 38 placed under the control of a transfercontrol stage 40 which is also adapted to receive the times du,.

The buffer memory 38 is adapted for containing three successive seriesof six times of sets-references: a central series which defines themeasurement horizon during an analysis, a front series which precedesthis central series in time and a rear series which follows it. At thearrival of a new time duo, the transfer control stage 40 is adapted fortransferring to the following stages the six times referenced du₀, . . ., du₅ of the central series as well as, under the reference du₋₁, thetime du₅ of the last set of the front series and, under the referencedu₊₁, the time du₀ of the first set of the series which has justarrived.

A first calculation stage 42, which receives these eight successivetimes, is programmed to select the six times referenced du₀, . . . du₅and to calculate their sum, which is the instantaneous period T of anangular range of combustions. Each new value T so calculated isaddressed to a buffer memory 44 where it replaces the value calculatedpreviously.

A second calculation stage 46 which receives these eight successivetimes (du₋₁, du₀, . . . , du₅, du₊₁) is programmed to select the sixfollowing times: du₋₁, du₀, du₂, du₃, du₅ and du₊₁ and to combine themaccording to the relation:

    Qc=2du.sub.0 -du.sub.2 +2du.sub.5 -du.sub.3 -du.sub.+1.

The term Q_(c) so calculated is addressed to a buffer memory 48 where itremains until a new value of Q_(c) arrives. The buffer memory 48 isconnected to a third calculation stage 50 which also receives from amemory 52, the weighting constant p=π/2√3. The calculation stage 50 isadapted for the calculation of the product D_(c) =p·Q_(c) and for itsapplication to a fourth calculation stage 54.

This calculation stage 54 also receives two constants A and B from amemory 56, which are experimentally determined and the term T from thebuffer memory 44. From these two magnitudes, the stage 54 calculates thegas torque, corrected for low-frequency perturbations, according to theequation Cg_(c) =A·D_(c) /T³ +B/T². The torque Cg_(c) so obtained iscorrected for low-frequency perturbations.

As mentioned in the preamble of the present description, the formulaused for the calculation of the mean gas torque, that is Cg=A·D/T³ +B/T²is only valid for engines operating at low-level condition. In the caseof an engine operating at high-level conditions, a correction must beapplied to the coefficient A in question, as indicated in U.S. Pat. No.9,111,273 referred to in the preamble. For this purpose, the coefficientA is replaced by A_(c) =A(1-z) with z=(fi/fr)². In this relation fi=1/T,the instantaneous frequency of the combustions, and fr is the torsionalresonance frequency of the shaft/inertial flywheel connection. To usethis correction in the context of the present invention, the memory 56will contain the constant term fr and the calculation stage 54 willcalculate fi=1/T and then z=(fi/fr)² and then A_(c) =A(1-z), and then,finally, the desired value Cg_(c) =A_(c) ·D/T³ +B/T², which, in thatcase, will be valid both for high- and low-level operating conditions ofthe engine and corrected for low-frequency perturbations.

According to the present invention, the embodiment represented in FIG. 4comprises, in addition, a sensor 58 which senses the atmosphericpressure Pa, a pressure sensor 60 Pc in the air-intake manifold, and abuffer memory 62 to which are applied the data produced by the pressuresensors 58-60. These two pressure sensors will be, for example, of thetype with strain gauge diffused in a silicon chip. First, they producean analog magnitude which is representative of the pressure measured.This magnitude is then converted into a numerical value by anincorporated analog/digital converter before being applied to the buffermemory 62. This buffer memory 62 is adapted for holding at any timethree successive measurements of the pressure Pc made during the courseof three successive combustion intervals. These measurements are thelast measurement received Pc.sub.(n') and the two preceding measurementsPc.sub.(n'-1) and Pc.sub.(n'-2), each measurement being identified byits rank n', (n'-1) or (n'-2). The buffer memory 62 is placed under thecontrol of a calculation stage 64 which communicates the four pressuredata which it contains to it. The calculation stage 64 is adapted forthe calculation of the term

    H.sub.n' =-δ·R.sub.N ·(Pc.sub.(n'-2) +Pc.sub.(n'-1) +α·(Pc.sub.(n'-2) -Pa)

from three of the four above-mentioned pressure data elements and threeconstants δ, R_(N) and α stored in a permanent memory 66. The values ofthese constants have been indicated above.

A last calculation stage 68 receives, on the one hand, the value Cg_(cl)produced by the calculation stage 54 and, on the other hand, the valueof the term H_(n') calculated by the calculation stage 64 as well as aconstant h which is also stored in the memory 66. The calculation stage68 is adapted for the calculation of the desired value Cg_(cn'2)according to the relation

    Cg.sub.cn'2 =h·Cg.sub.cn'1 +H.sub.n'.

As indicated above, the magnitude Cg_(n'2) thus obtained is thecompletely corrected numerical value of the torque of a four-stroke,four cylinder internal combustion engine of injection, which operates atlow- and high-level operating conditions, this value being in fact alsocorrected for low-frequency perturbations which affect the engine aswell as for errors caused by the particular conditions of thecombustions in the engine (rate of recirculation of the exhaust gases,rate of residual gases, excess of fuel and transitory regimens) . Asindicated above, the invention can be implemented using a measurement ofthe air flow rate of the collector, instead of a pressure measurement.The particular means of production of this variant are represented inFIG. 5.

According to FIG. 5, a mass flow sensor 70 is placed in the air-intakemanifold. This sensor 70 will be, for example, of the type with hot wireor with embedded elastic blade at one end. The sensitive elements ofthese sensors are mounted in a bridge, so as to produce first an analogsignal, which is then transformed into a digital value incorporatedanalog/digital converter. This digital value is then applied to a buffermemory 72, which is adapted for holding at any time three data elementsD_(n'), D_(n'-1) and D_(n'-2), which are representative, respectively,of the air flow rates in the intake manifold, during the combustioninterval of rank n' during the course of an analysis, and of the twocombustion intervals which precede it. The data stored in the buffermemory 72 is applied to a calculation stage 74 which also receives fromthe buffer memory 44, the period T of the combustion interval during ananalysis (this period is practically constant over the three successiveperiods concerned). The calculation stage 74 is adapted for thesuccessive calculation of the terms (D_(n'-1) ·T) and (D_(n'-2) ·T) andfor applying them to a buffer memory 76. The two latter terms arerespectively M_(n'-1) and M_(n'-2), as already indicated above(recalling that T=1/2N) . Moreover, the data element D_(n'-2) stored inthe buffer memory 72 is applied to a calculation stage 78 adapted forcalculating (D_(n'-2) ·T-M₀) from D_(n'-2) and from M₀, the air massintroduced into a cylinder for a fully opening butterfly valve, which isa measured constant, stored in a permanent memory 80. The term (D_(n'-2)·T-M₀) so calculated is Cp.sub.(n'-2). This term is then applied to abuffer memory 82.

The constant terms δ, α and h defined above are stored in a permanentmemory 84. The terms (D_(n'-1) ·T) and (D_(n'-2) ·T) stored in thebuffer memory 76, the term (D_(n'-2) ·T-M₀) stored in the buffer memory82 and the constants δ and α stored in the permanent memory 84 areapplied to the calculation step 86 which is adapted for the derivationof the above-mentioned term H_(n). In this stage 86, the relationexpressing H_(n) is:

    H.sub.n' =-δ·(D.sub.n'-1 ·T+D.sub.n'-2 ·T)+α·(D.sub.n'-2 ·T-M.sub.0)

This relation is equivalent to the one used above with datarepresentative of the pressures in the air collector and of theatmospheric pressure.

During the period of analysis of rank (n'-2), data is produced,Pc.sub.(n'-2) and D.sub.(n'-2), which allow, on the one hand, thecalculation of the pumping torque Cp.sub.(n'-2) of the cylinder whichwill be in release during the period of analysis of rank n' and, on theother hand, the air mass M.sub.(n'-2) which will participate in thecombustion effected during this period of rank n'. During the period ofanalysis of rank (n-1) , data Pc.sub.(n'-1) or D.sub.(n'-1) are producedwhich allow the calculation of the compression torque of the cylinderduring compression, during the period of analysis of rank n', which willbe in release during the period of analysis of rank (n'+1); thiscompression torque is proportional to M.sub.(n'-1).

This pumping torque and this compression torque, as well as this airmass participating in the combustion during the period of analysis ofrank n' are directly dependent on the particular conditions of thecombustions. Taking them into account allows the correction for theeffects on the Cg of the rate of recirculation of the exhaust gases, ofthe rate of residual gases burned, of the excess fuel and of thetransitory operating conditions of the engine.

The invention is not limited to the described examples. As a variant, itis possible to calculate Cg from the general relation defining D,instead of from the simplified relation used in the described example.Similarly, it will be possible, in some cases, not to use thecorrections pertaining to the low-frequency perturbations and/or thecorrections concerning the high-level engine operating conditions.Moreover, to take into account the limited variations in the fillingcoefficient of the cylinders as a function of the speed of rotation ofthe engine, a correction circuit receiving the mean value R of thiscoefficient and the period of the combustions T can be provided, whichwill produce R_(N) from determined experimentally mapping. Such acircuit will be placed between the memory 66 and the calculation stage64.

We claim:
 1. Method for the production of a digital value Cg which isrepresentative of the mean gas torque generated by each combustion ofthe gas mixture in the cylinders of a combustion engine, the combustionengine includes measurement references arranged on a ring gear which isintegrally connected to an inertial flywheel of the combustion engine orits crankshaft, means to define at least one reference for indexing themeasurement references, a sensor to sense the passage of the measurementreferences, which is fixedly mounted in a vicinity of the ring gear,said method comprising the steps of:producing a primary digital valued_(i) which is representative of an instantaneous passage of time sensedby the sensor of each of the measurement references; deriving, from theprimary digital values d_(i), a first secondary digital value T, whichis representative of the total passage of time before the sensor of eachseries of n references defining an angular range of the combustions inthe combustion engine; deriving a second secondary digital value D,which is representative of a projection onto a phase reference line ofthe means to define at least one reference for indexing the measurementreferences, corresponding to an origin of the angular range of thecombustions, of an amplitude of an alternating component of theinstantaneous passage times di of the measurement references sensed bythe sensor at a frequency of the combustions in the combustion engine;deriving the desired numerical value Cg from the relation Cg=A·D/T³+B/T² in which A and B are experimentally determined constants;establishing a measurement horizon equal to at least the angular rangebetween two consecutive explosions in the combustion engine; regroupingthe instantaneous passage times di of the references within thismeasurement horizon in a relatively small number of passage times du₀, .. . , du_(m) of reference sets and of identifying these times du by therank O . . . m in each measurement horizon during the course of ananalysis; combining together by addition and subtraction, possiblyweighted, a given number of times having determined ranks, so as toproduce a magnitude Q having a mean value which is equal to zero and afrequency response which is nonzero at the analysis frequency of thecombustion engine explosions; and determining the weighting constant psuch that the term D=p·Q obtained by a simplified calculation has afrequency response, at least for said frequency of analysis and for thecombination of the times used to express Q, which is essentiallyidentical to that obtained by the term: ##EQU2##
 2. Method according toclaim 1, wherein the number of reference sets within a measurementhorizon is an even number, and wherein an angular length of these setsare equal, and wherein the number of passage times of reference setscombined to produce Q is a even number equal to at least four.
 3. Methodaccording to claims 1 or 2,wherein the frequency response of the termD=p·Q is equal to or less than four times said analysis frequency, whichis essentially identical to that initially obtained.
 4. Method accordingto claim 1, wherein the measurement horizon includes a small number ofreferences located on both sides of the angular range between twoconsecutive explosions in the combustion engine.
 5. Method according toclaim 1, wherein the reference sets of a measurement horizon do not haveexactly the same length.
 6. Method according to claim 1, wherein themeasurement horizon is exactly defined by the angular range separatingtwo explosions in the combustion engine, and wherein the number ofreference sets is six, and the six measured times referenced are du₀, .. . , du₅, and the magnitude Q=(du₀ -du₂ -du₃ +du₅) and the weightingconstant p=π2√3, when the fixed sets have the same angular length π/6.7. Method according to claim 1, wherein the angular range between twoconsecutive explosions is cut into six sets of identical angular length,and wherein the measurement horizon is equal to seven consecutivereference sets du₀. . . , du₆, and wherein the magnitude Q is equal toQ=du₀ -du₃ +3/2·(du₆ -du₄).
 8. Method for the production of a firstnumerical value Cg which is representative of the mean gas torquegenerated by each combustion of the gaseous mixture in the cylinders ofa combustion engine and a second numerical value δCg which isrepresentative of the variations of resistant torque applied to a two-or four-cylinder engine, the combustion engine includes measurementreferences arranged on a ring gear which is integrally connected to aninertial flywheel of the combustion engine or its crankshaft, means todefine at least one reference for indexing the measurement references, asensor to sense the passage of the measurement references, mounted inthe vicinity of the ring gear, said method comprising the stepsof:producing a primary numerical value d_(i) which is representative ofan instantaneous passage of time sensed by the sensor of each of themeasurement references; deriving, from the primary numerical valuesd_(i), a first secondary numerical value T which is representative ofthe total passage of time before the sensor of each series of nreferences defining an angular range of the combustions in thecombustion engine; deriving a second secondary numerical value D, whichis representative of a projection on a phase reference line of the meansto define at least one reference for indexing the measurementreferences, corresponding to an origin of the angular range of thecombustions, of an amplitude of an alternating component of theinstantaneous passage times di the measurement references sensed by thesensor at a frequency of the combustions in the combustion engine;deriving the desired numerical value Cg from the relation Cg=A·D/T³+B/T² in which A and B are experimentally determined constants; andwherein the method for the production of said second value δCg comprisesthe sub-steps of establishing a measurement horizon equal to at leastthe angular range between two consecutive explosions in the combustionengine, regrouping the instantaneous passage times di of the referenceswithin this measurement horizon in a relatively small number of passagetimes du₀, . . . , du_(m') of reference sets and in identifying thesetimes du by the rank 0 . . . m' in each measurement horizon during thecourse of an analysis, the angular values of the time sets of rank 0 andm' being equal, assigning the reference du₋₁ to the time of the lastreference set of the last measurement horizon analyzed earlier and thereference du₊₁ to the time of the first reference set of the nextmeasurement horizon analyzed, combining four of these times du accordingto the relation q=(du₀ -du₋₁ +du_(m') -du₊₁), and deriving the desiredterm δCg according to the relation δCg=a·q·A/T³, where A is a newconstant dependent on the angular value of the four given referencesets.
 9. Method according to claim 8, wherein the measurement horizon isexactly defined by the angular range separating two explosions in thecombustion engine, and wherein the number of reference sets in themeasurement horizon is six and the angular value of each set is π/6, andthe constant a=π/2√3.
 10. Method according to claim 8, wherein theangular range of the reference sets of times reference times du₀ anddu_(m') is relatively large to produce a more precise term δCg, themeasurement horizons present a slight phase lead with respect to theintervals of high dead centers of the combustion engine.
 11. Methodaccording to claims 6 or 8, wherein, to produce a term Q, corrected forlow-frequency perturbations generated by variations of a resistanttorque applied to the combustion engine, this term is calculatedaccording to the relation:

    Qc=(Q+q)=(2du.sub.0 -du.sub.-1 -du.sub.2 -du.sub.3 -du.sub.+1 +2du.sub.5).


12. Method for the production of a numerical value Cg_(c) which isrepresentative of the mean gas torque, generated by each combustion ofthe gaseous mixture in the four cylinders of a four-stroke combustionengine, and corrected for the influences of the particular conditions ofthese combustions, said combustion engine includes measurementreferences arranged on a ring gear which is integrally connected to aflywheel of the combustion engine or its crankshaft, means to define atleast one reference for indexing the measurement references, a sensor tosense the passage of the measurement references, mounted in a fixedmanner in a vicinity of the ring gear, said method comprising the stepsof:producing a primary numerical value di which is representative of aninstantaneous passage of time sensed by the sensor of each of themeasurement references; deriving, from the primary numerical valuesd_(i), a first secondary numerical value T which is representative ofthe total passage of time before the sensor of each series of mreferences defining an angular range of the combustions in thecombustion engine; deriving a second secondary numerical value D, whichis representative of a projection onto a phase reference line of themeans to define at least one reference for indexing the measurementreferences, corresponding to an origin of the angular range of thecombustions, of an amplitude of an alternating component of saidinstantaneous times d_(i) at the frequency of the combustions in thecombustion engine; deriving an intermediate numerical value Cg from therelation Cg=A·D/T³ +B/T² in which A and B are experimentally determinedconstants; measuring, especially in the air-intake manifold of thecombustion engine, physical parameters which allow a determination of anair mass M pumped into a cylinder during the period of combustion ofanother cylinder, as well as a pumping torque Cp required for thispurpose; storing in a memory the values of these physical parameters orthose of the magnitudes M and Cp, during the following two periods ofcombustion; combining the data so stored in the memory to produce a termH_(n) ' for the correction of the torque Cg_(n') attributed to theperiod of combustion of rank n according to the relation H_(n')=-δ(N_(n'-2) +M_(2n'-1))+α·Cp.sub.(n'-2), where δ and α are constantswhich depend on the type of combustion engine; and calculating thecorrected mean gas torque, generated during the period of combustion ofrank n, according to the equation Cg_(cn') =h·Cg_(n'), where h is acalibration constant which is dependent on the type of combustionengine.
 13. Method according to claim 12, wherein determination of theair mass M includes measuring the pressure Pc in the air-intake manifoldof the combustion engine and in calculating M according to the relationM=Pc·R_(N), where R_(N) is the coefficient, which is essentiallyconstant as a function of the speed N of the combustion engine, offilling of the cylinders of the combustion engine, and whereindetermination of the pumping torque Cp includes measuring theatmospheric pressure Pa and in calculating Cp according to the relationCp=(Pc-Pa).
 14. Method according to claim 12, wherein determination ofthe air mass M includes measuring the mass flow Da of the air in themanifold and in calculating M according to the relation M=Da·T, where Tis the period of the combustions, and wherein determination of thepumping torque Cp consists in calculating Cp according to the relationCp=(Da·T-M₀), where M₀ is the air mass introduced into a cylinder by afully opened butterfly valve.
 15. Method according to one of claims 12,13, or 14, wherein the term D of the relation defining Cg is obtained bythe performance of the following steps:establishing a measurementhorizon equal to at least the angular range between two consecutiveexplosions in the combustion engine and dividing this measurementhorizon in a relatively small number of reference sets; calculating thepassage times of each of these reference sets before the sensor andranking them in each measurement horizon; combining together, byaddition and subtraction, a given number of times having predeterminedranks, so as to produce a magnitude Q having a zero mean value and anonzero frequency response at the analysis frequency of the explosionsof the motor; and determining a weighting constant p such that the termD=p·Q obtained by a simplified calculation has a frequency of responseat least for said analysis frequency and for the combination of thetimes used to express Q, which is essentially identical to that obtainedby a term ##EQU3##
 16. Method according to claim 15, wherein the angularvalue of each reference set is π/6.
 17. Method according to claim 15,further comprising a term D_(c) =p·Q_(c) corrected for the low-frequencyperturbations which affect the combustion engine, each reference setmeasures π/6, the constant p=π/2√3 and the value of the term Q socorrected is Qc=(2du₀ -du₋₁ du₂ -du₃ -du₊₁ +2du₅), with du₋₁ and du₊₁,the respective passage times of the sets arranged at a given instant onboth sides of said angular range.
 18. Device for the production of anumerical value Cg which is representative of the mean gas torquegenerated by each combustion of the gaseous mixture in the cylinders ofa combustion engine at low-level operating conditions, the combustionengine includes measurement references arranged on a ring gear which isintegrally connected to an inertial flywheel or a crankshaft of thecombustion engine, means to define at least one reference for indexingthe measurement references, a sensor to sense the passage of themeasurement references which is mounted in a fixed manner in a vicinityof the ring gear, said device comprising:calculation means to produce aprimary numerical value d_(i) which is representative of aninstantaneous passage of time sensed by the sensor of each of themeasurement references; calculation means to derive from the primarynumerical values d_(i) a first secondary numerical value T which isrepresentative of a total passage time before the sensor of each seriesof n references defining an angular range separating two consecutivecombustions in the combustion engine; calculation means to derive asecond secondary numerical value D which is representative of aprojection, onto a phase reference line of the means to define at leastone reference for indexing the measurement references, corresponding toan origin of the angular range of the combustions, of an amplitude of analternating component of the instantaneous passage times di of themeasurement references sensed by the sensor at a frequency of thecombustions in the combustion engine; calculation means to derive thedesired numerical value Cg from the relation Cg=A·D/T³ +B/T² in which Aand B are experimentally determined constants, contained in a memory;processing and calculation means to establish a measurement horizonequal to at least said angular range, to regroup the instantaneouspassage times d_(i) of the references within this measurement horizon ina relatively small number of passage times du₀, . . . , du_(m) ofreferences sets and to define these times du by their rank (0 . . . m)in each measurement horizon; calculation means to combine together, byaddition and subtraction, a given number of set times havingpredetermined ranks, so as to produce a magnitude Q having a zero meanvalue zero and a nonzero frequency response at the analysis frequency ofthe explosions of the combustion engine; calculation means to producethe term D=p·Q from the value Q calculated earlier and a weightingcoefficient p determined experimentally and stored in a memory, thevalue of p and the combination of the times used to express Q havingbeen determined so that the term D so obtained by simplified calculationhas a frequency response, at least for said analysis frequency, which isidentical to that obtained for the term: ##EQU4##
 19. Device to producea first numerical value Cg which is representative of the mean gastorque generated by each combustion of the gas mixture in the cylindersof a combustion engine operating at low-level condition, and a secondnumerical value δCg representative of the variations of the resistanttorque applied to such an engine comprising two or four cylinders, saidcombustion engine includes measurement references arranged on a ringgear which is integrally connected to a flywheel or a crankshaft of thecombustion engine means to define at least one reference for indexingthe measurement references a sensor to sense the passage of themeasurement references, which is mounted in a fixed manner in a vicinityof the ring gear, said device comprising:calculation means to produce aprimary numerical value d_(i) which is representative of aninstantaneous passage of time sensed by the sensor of each of themeasurement references; calculation means to derive from the primarynumerical values d_(i) a first secondary numerical value T which isrepresentative of a total passage time before the sensor of each seriesof n references defining an angular range separating two consecutivecombustions in the combustion engine; calculation means to derive asecond secondary numerical value D which is representative of aprojection, onto a phase reference line of the means to define at leastone reference for indexing the measurement references corresponding toan origin of the angular range of the combustions, of an amplitude of analternating component of the instantaneous passage times d_(i) of themeasurement references sensed by the sensor at a frequency of thecombustions in the combustion engine; and calculation means to derivethe first desired numerical value Cg from the relation Cg=A·D/T³ +B/T²in which A and B are experimentally determined constants contained in amemory, wherein said device to produce said second value δCg furthercomprises,processing and calculation means to form a measurement horizonequal to at least one angular range between two consecutive explosionsin the combustion engine, to regroup the instantaneous passage timesd_(i) of the references within this measurement horizon in a relativelysmall number of passage times du₀, . . . , du_(m) of reference sets andto identify these times du by the rank 0 . . . m' in each measurementhorizon during the course of an analysis, the angular values of thereference sets of the times of rank 0 and m' being equal, means to storein memory the times du₀, . . . , du_(m) ' as well as, on the one hand,the time of last reference set of the last measurement horizon analyzedpreviously and to assign it the reference du₋₁ and, on the other hand,the time of the first reference set of the next measurement horizonanalyzed and to assign it the reference du₊₁, means to produce a term qaccording to the relation q=(du₀ -du₋₁ +du_(m') -du₊₁), and means toderive the desired term δCg according to the relation δCg=a·q·A/T³ whereA is a constant which depends on the angular value of the four referencesets concerned.
 20. Device for the production of a numerical value Cgwhich is representative of the mean gas torque generated by eachcombustion of the gaseous mixture in the four cylinders of a four-strokecombustion engine at low-level operating conditions, said value beingcorrected for influences of the particular conditions of thesecombustions, said combustion engine includes measurement referencesarranged on a ring gear which is integrally connected to an inertialflywheel or a crankshaft of the combustion engine, means to define atleast one reference for indexing the measurement references, a sensor tosense the passage of the measurement references mounted in a fixedmanner in a vicinity of the ring gear, said devicecomprising:calculation means to produce a primary numerical value d_(i)which is representative of an instantaneous time of passage time sensedby the sensor of each of the measurement references; calculation meansto derive from the primary numerical values d_(i) a first secondarynumerical value T which is representative of a total passage time beforethe sensor of each series of m references defining an angular rangeseparating two consecutive combustions in the combustion engine;calculation means to derive a second secondary numerical value D whichis representative of a projection, onto a phase reference line of themeans to define at least one reference for indexing the measurementreferences, corresponding to an origin of the angular range ofcombustions, of an amplitude of an alternating component of theinstantaneous passage times d_(i) of the measurement references sensedby the sensor at a frequency of the combustions in the combustionengine; calculation means to derive an intermediate numerical value Cgfrom the relation Cg=A·D/T³ +B/T², where A and B are experimentallydetermined constants, contained in a memory; means including sensorsinstalled in an air-intake manifold to determine an air mass M pumpedinto a cylinder during the course of the period of combustion of anothercylinder; means to determine the pumping torque Cp required for thispurpose; means to store in memory the data M and Cp or the constituentelements of these data during the two following combustion periods;means to combine this data or its constituent elements to produce a termH_(') of correction of a torque Cg_(n') pertaining to the period ofcombustion of rank n according to the relation, H_(n) '=-δ·(M_(n'-2)+M_(2n'-1))+α·Cp.sub.(n'-2), in which δ and α are constants which aredependent on the type of combustion engine, calculation means tocalculate the corrected mean gas torque, generated during the course ofthe combustion period of rank n', according to the relation, Cg_(cn')=h·Cg_(n) +H_(n'), in which h is a calibration constant which isdependent on the type of combustion engine; and the constants δ, α and hbeing stored in a permanent memory.